The present invention relates generally to radiation detectors and methods. More specifically, the present invention relates to radiation detection devices and methods, including radiation detectors having beam-oriented pixellated scintillators capable of high-performance, high resolution imaging.
Scintillation spectrometers are widely used in detection and spectroscopy of energetic photons and/or particles (e.g., X-rays and gamma-rays). Such detectors are commonly used, for example, in nuclear and particle physics research, medical imaging, diffraction, non destructive testing, nuclear treaty verification and safeguards, nuclear non-proliferation monitoring, and geological exploration.
A wide variety of scintillators are now available and new scintillator compositions are being developed. Among currently available scintillators, thallium-doped alkali halide scintillators have proven useful and practical in a variety of applications. One example includes thallium doped cesium iodide (CsI(Tl)), which is a highly desired material for a wide variety of medical and industrial applications due to its excellent detection properties, low cost, and easy availability. Having a high conversion efficiency, a rapid initial decay, an emission in the visible range, and cubic structure that allows fabrication into micro-columnar films (see, e.g., U.S. Pat. No. 5,171,996), CsI(Tl) has found use in radiological imaging applications. Furthermore, its high density, high atomic number, and transparency to its own light make CsI(Tl) a material of choice for medical imaging applications, such as X-ray and gamma-ray spectroscopy, Single Photon Emission Computed Tomography or SPECT, positron emission tomography (PET), and the like.
Scintillation spectrometry generally comprises a multi-step scheme. Specifically, scintillators work by converting energetic particles such as X-rays, gamma-rays, and the like, into a more easily detectable signal (e.g., visible light). Incident energetic photons are stopped by the scintillator material of the device and, as a result, the scintillator produces light photons mostly in the visible light range that can be detected, e.g., by a suitably placed photodetector. The detected light photons from the scintillator can then be processed and converted into other signals and thus can be used in generating an image, such as an image of a patient or a portion of the patient's body (e.g., internal organs, etc.).
Many nuclear medicine imaging techniques, such as SPECT and PET, require high spatial resolution in order to generate a desired image due, for example, to factors such as the small scale of the details being imaged, as well as the complexity of the detection and estimation tasks. Unfortunately, existing medical imaging instrumentation, such as SPECT instrumentation, is often restrictively expensive and often does not provide the required performance needed for certain applications, such as study and analysis of biological processes and activity of pharmaceutical agents in vivo. As such, the development of a high-resolution detector combined with energy discrimination capabilities is essential for the improvement of future imaging devices
For example, one important factor limiting high-resolution radiation imaging in existing systems is the high potential for parallax errors that degrade and/or limit image quality. Parallax errors or depth of interaction (DOI) errors occur when an energetic photon strikes the detector surface at a given angle of incidence (angle θ). Where the scintillator material has a linear attenuation coefficient μ, and the mean depth of interaction is given by μ−1 and the linear displacement due to parallax error in a direction parallel to the surface of the scintillator can be calculated as μ−1 sin θ. Parallax errors for imaging lower energy radiation sources are less significant and generally smaller than the spatial resolution limit imposed by realistic values of a collimator pinhole diameter (e.g., >100 μm). However, for imaging higher energy photons (e.g., gamma-rays), these errors are significantly large, resulting in a significant degradation of spatial resolution.
Parallax error can be a fundamental problem in many radiation imaging systems having conventional scintillators or even with existing high-resolution, microcolumnar CsI(Tl) scintillators, particularly where a high spatial resolution is desired. For example, the parallax errors arising from the depth of penetration of the incident energetic photons (e.g., gamma-rays), such as in radionuclide imaging using a pinhole collimator and existing scintillators, can result in an undesirable line pattern in a generated image rather than a well defined point-like emission of light, substantially degrading performance of the detectors, including spatial resolution.
Thus, there is a need for improved scintillators and radiation detection and imaging devices, as well as related methods, including scintillators and radiation detectors capable of high-resolution, high performance imaging.